Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

readOnlyHint=true is already declared, but the description reinforces it in domain terms ('Non-mutating (no mail sent)') and, with no output schema present, usefully discloses what comes back: deliverability, corrected components, and a confidence score. It does not cover failure behavior for undeliverable addresses or rate limits, keeping it short of a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three tight sentences, front-loaded with purpose and followed immediately by the invocation fork and the safety/return note. The API endpoint mention is the only marginally expendable clause, and it costs almost nothing.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema and six optional parameters, the description carries the key burdens well: it explains the input modes and summarizes the return payload. It stops short of covering what happens on an undeliverable result or authentication requirements, so it is strong but not exhaustive.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 83%, so the baseline is 3, and the description adds genuine meaning beyond the schema by explaining the either/or relationship between freeform `address` and the structured `primary_line`/`city`/`state`/`zip_code` set. That resolves the ambiguity created by zero required parameters. It does not address `secondary_line`, which the schema documents.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb pair ('Validate & standardize') and resource ('a US address'), plus the concrete outputs (deliverability, corrected components, confidence score). It is readily distinguishable from lob_verify_intl_address and lob_us_autocomplete by the explicit 'US' scope and validation framing.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It clearly specifies how to invoke the tool with either a freeform `address` or structured fields, which is real invocation guidance. However, it never says when to prefer this over lob_us_autocomplete (type-ahead) or lob_verify_intl_address (non-US input), so sibling routing is left to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.